Blake Shelton, Gwen Stefani pack on the PDA during performance

Gwen Stefani and Blake Shelton showed off their clear chemistry as the couple performed a duet at an intimate and star-studded Hamptons event.

Stefani was a headline performer at Saturday night’s Apollo in the Hamptons gala, at billionaire Ron Perelman’s Creeks estate in East Hampton.

But she surprised the power crowd – which included Jennifer Lopez, Usher, Pharrell Williams, Jack Nicholson, Patriots owner Bob Kraft and Jon Bon Jovi – by bringing along Shelton and performing on stage with him.

Lyrics in the song, which they wrote together, include, “I never ever meant to get so into you/Thought I was using you just to get me through/You know I’m broken I don’t trust anyone/Last Thing I needed was to fall in love.”

Stefani and Shelton’s romance blossomed on the set of “The Voice” after they both went through painful splits and respective divorces from Gavin Rossdale and Miranda Lambert.

He had told ‘Today’ about the tune, “We were just writing it about….it was hard to kind of let our guards down again, you know what I mean? Just going through some issues, and so that’s what the song was even written about.” He added, “Its like, I know something bad is going to happen, because it always does, so let’s just get it over with now…at some point you’re, like….’It just is what it is now, so let’s go for it.”

Sources tell Page Six that Shelton was a secret, last minute addition to Stefani’s show in the Hamptons, and he even had to borrow a guitar from Bon Jovi.

Shelton had earlier sat with his arms around Stefani during performances in Perelman’s barn from stars including Pharrell, Ciara, Bon Jovi and Eagles legend Joe Walsh.

And after performing their duet, Shelton then stood front row for the rest of Stefani’s set – which included hits such as “Hollaback Girl” and “Don’t Speak” – and he was seen cheering, clapping and even playing air guitar to her songs.

Urging the crowd to participate, Stefani said, “The tall guy stood up first, good job Blake.” Following her show, the romantic couple slipped out before Lionel Ritchie and then Usher took the stage.

Just a few hundred lucky guests were present at the Apollo ‘Night of Legends’ – described as the ultimate Hamptons event of the summer – which was hosted by Perelman, Kraft, Bon Jovi and Dick Parsons and raised $5 million for music and educational programs for kids at the historic Harlem theater.

Power players in the room included NBCUniversal chairman Ron Meyer, music guru Irving Azoff Blackstone’s Steve Schwarzman and wife Christine, hedge fund billionaire David Tepper, David Zaslav, New York Governor Andrew Cuomo, with Sandra Lee, media mogul Jay Penske with Elaine Irwin, NYC attorney general Eric Schneiderman and Colin Powell. They mingled with stars including Lopez – who was with her manager Benny Medina – Don Johnson, John McEnroe, Christie Brinkley, Charlie Rose and Penny Marshall.